Lubricating oil composition



' Patented F b. 12, 1946 UNITED STATE PATENT OFFICE,

nunaroarmo on. coMr'osrrroN Anthony H. Gleason, Westfleld, N. .L, assignor to Standard Oil Development Company, a corporation of Delaware No Drawing. Application December 31, 1942,

Serial No. 470,810

8 Claims. (Cl. 252-56) This invention relates to mineral lubricating oil compositions of good viscosity characteristics. It relates particularly to the blending of new type synthetic compounds in mineral lubricating oils,

. thereby establishing a lower rate of change of viscosity with temperature upon the blended oil than upon the unblended oil.

Viscosity, as one of the more important physical properties of a lubricating composition, is signifi cant as to its actual value at a particular temperature and as to its rate of change with temperature. In the petroleum industry, the significance of the first aspect is indicated by the S. A. E. number and the second by certain established scales, such as viscosity index, viscosity gravity constant and viscosity pole height. I

One of the outstanding scales for evaluating lubricating oils upon the basis of their viscosity temperature variation is that advanced by Dean ceptionally high rate of viscositychange was rated as zero.

.If an oil has a low viscosity index, that is, the viscosity changes rapidly with changes in temperature, it may be viscous enough to function satisfactorily at one temperature from the point of view of viscosity, but wholly unsatisfactory at another temperature because of the low viscosity or body of the oil. Another oil of low V. I. characteristic may be satisfactory at engine operating temperatures for automobile performance, but wholly unsatisfactory at low temperatures in Presenting difiiculty of starting the engine due to its extremely high viscosity, rendering it difiicult to move the engine parts with the power available. 4

Of the various types of lubricating oil distillates tent, however, such as by solvent extraction or heavy acid treatment, is usually costly. Also, when oils are extensively treated, the thus treated oils are less chemically stable. Such chemical instability is shown in service and in laboratory testin for resistance to oxidation and corrosion towards alloy bearings. Usually, therefore, it is considered more commercially advantageous to refine oils according to general standard and to eflect further improvements as considered advisable by the addition of particularly effective compounds such as, in this case, the addition of compounds particularly efl'ective to improve viscosity index.

A number of lubricating oil addition agents which reduce the viscosity temperature variation ofoils are already well-known in the art. A

compound to be advantageous as a viscosity index improver has to be satisfactorily soluble in mineral lubricating oils, efiective in low concen- .trations and substantially stable under conditions of usage to which a blended'composition is subjected in service.

A class of compounds which have been extensively investigated is the linear chain, two-dimensional, polymeric compounds having molecular weights above 800. By the term linear chain,

two-dimensional, polymeric compound" is designated that class of polymeric compounds which are theoretically visualized as consisting of long chains or threads in contrast to the so-called three-dimensional polymers, in which molecular growth is visualized as having been effected by derived from crudes, the paraffinic base oils have the best general viscosity characteristics, while those of naphthenic base have the poorest viscos-' a preferred range from 0.75% to 3.0%. The polyfining to improve viscosity index to any great exreactions in three dimensions. The physical dif: ference between the two types of polymersis that with the linear polymers, the physical characteristics are more of the nature of viscous liquids, while those of the three-dimensional polymers are more or less resinous compounds insoluble in mineral lubricating oils. In High Polymers" collected papers of W. H. 'Caruthers (Mark 8: Whitby), vol. I, page 15, linear polymers are considered characterized by a recurring structural unit, usuallya bivalent radical. The polymeric compound of this invention is considered to be a condensation or C polymer, that is, a polymeric molecule formed from monomeric compounds by a process of polyintermolecular condensations.

In accordance with the present invention, high molecular weight polyesters derived by the condensation of certain dibasic. acids and glycols have been found to be advantageous as viscosity index improvers for lubricating oils in concentrations between 0.5% and 5.0% by weight and as esters of this'invention are formed by the condensation of succinic acids which are preferably alkylated, with a glycol which may or may not be alkylated. The condensation products, are predominantly linear in structure and are completely soluble in lubricating oils. The reaction may be formulated as follows:

where R1 is an alkyl or alkene group having at least six carbon atoms and preferably between eight and eighteen. R: and B: may be hydrogen atoms or alkyl groups and u must be greater than one, and a: and a may be or an integer. If R: and R: represent alkyl groups containing up to about carbons, the solubility of the resultant polyester in lubricating oils is increased, especially if R1 is small. 0n the other hand, R2 and Rs may both be hydrogen atoms without adversely aiiecting the solubility of the polyester in mineral oils, provided R1 is sufiiciently large, that is, at least about 10 carbon atoms.

In practice it is preferable to use a glycol of the a, or type. When such glycols are employed, the condensation proceeds smoothly and without the undesirable elimination of water and the formation thereby of an alkenol. The particular disadvantage of the formation of alkenols is that the linear chain formation is interrupted. However, by maintaining a reaction temperature of less than about 200 0., it is frequently possible to use a secondary or di-secondary glycol. Glycols with the OH groups on adjacent carbon atoms, such as are obtained by the hydration of alkene oxides or. hydrolysis of alkene halohydrins, are

not generally applicable because of the greatly increased tendency to form dimeric ring esters of the lactide type. Such esters are unreactive and the polyester compounds of little or no value as V. I, improvers.

In the general formula, the tendency of compounds to form rings decreases as 2: increases. It is preferred that a: has a value between 4 and 10. When the values of R1, R2 and Rs are within the preferred ranges, the percentage of oxygen in the polyesters is limited to between about 10% to 20%, and in this range they are satisfactorily soluble in mineral lubricating oils, and are very eiiecti-ve V. I. improvers in low concentrations, that is, between 0.5% and 5% by weight. Especially advantageous compounds are the linear polyesters formed from the reaction between a1- kylated succinic acid, in particular tri-isobutylene succinic acid and p-dodecyl tetramethylene glycol, hexamethylene glycol and decamethylene glycol.

To insure good mechanical stability of the polyesters, their average molecular weights are restricted to the range of 5,000 to 25,000. Their potency increases with molecular weight, but a point is always reached where the thermal and mechanical instability of the polyesters is sufilclently great to cause an appreciable drop in viscosity and V. I. of the blend with usage.

Alkylated succinic acids of the general formula HOzCCHaCHRrCOdI-I may be prepared from the dibromide of an a-olefln through the dinitrile or by condensing malonic ester successively with an alkyl halide and chloracetic ester followed by decarboxylaticn. It is much simpler, however, to prepare these acids by reacting an unsaturated hydrocarbon with maleic anhydride at a temperature of about 180 0. Thus, tri-isobutylene succinic acid was prepared by the addition of tri-isobutylene and maleic anhydride at C.

Any of the a, w glycols may be conveniently used in the condensation with the exception of ethylene and trimethylene glycols which form mainly the ring diesters. The glycols are generally prepared by the reduction of the esters of corresponding a, w dibasic acids. Useful glycols with a side chain can also be made by reduction of esters of the allnylated succinic acids described above. Thus, p-dodecyl tetramethylene glycol is made by the catalytic hydrogenation of the diethyl ester of tri-isobutylene succinic acid at 2,000 lbs. pressure. Glycols with one secondary hydroxyl group, which serves to increase the number of side chains in the resultant polyesters. are typifled by octadecane-l, 12-diol which is obtained by the hydrogenation of castor oil.

The formation of the polyesters is usually efiected by heating equimolecular quantities of the alkyiated succinic acid and the glycol at term peratures between and 230 0. together with vigorous agitation and simultaneous contact with a stream of dry, inert gas such as nitrogen or carbon dioxide.

Example parative data:

Saybolt 8a bolt vis. 100 F. vis. 10" I.

Mineral oil 8. A. E. 20W 275.8 45. 9 13 Mineral oil S. A.-E. 20W+2% polyester 378. 0 54. B 82 The above description and illustrative examples of the preparation and application of the compositions of the invention are presented for purposes of explanation but not of limitation of the invention. Modifications and variations can 7 be made therein without exceeding the scope of the invention. It is intended to claim broadly the invention and it is to be limited only by the following claims or their equivalents.

What is claimed is:

l. A lubricating composition comprising a min-- eral lubricating oil and a viscosity-index increasing amount of an oil-soluble linear polyester reaction product of equimolecular proportions of trl-isobutylene succinic acid and decamethylene glycol, said polyester having a molecular weight in the range of about 5,000 to 25,000.

2. A lubricating composition comprising a mineral lubricating oil and 0.5 to 5% of a linear oilsoluble polyester reaction product having a molecular weight from about 5,000 to 25,000 of a substituted succinic acid containing an alkyl group of 8 to 18 carbons atoms and a lycol.

3. Compcsition according to claim 2 in which the substituted succinic acid is tri-isobutylene lecuiar proportions of a substituted succlnic acid 10 substituted with a group selected from the class of alkyl and alkene groups of at least 6 carbon atoms, and a glycolhaving at least 4 carbon atoms between thehydroxyl groups said polyester having a molecular weight in the range of about,5,000 to 25,000.

6. Composition according to claim 5 in which the substituted suceinic acid is tri-isobutylene succinic acid.

7. Composition according to claim 5 in which the polyester is formed from an 02-10 glycol.

8'. Composition according to claim 5 in which the glycol is a polymethylene glycol.

ANTHONY H. GLEASON. 

